The present invention relates generally to spectrum display apparatuses and more particularly to a spectrum display apparatus which is used to operate in cooperation with graphic equalizers for variably adjusting the signal level of each of a plurality of divided frequency bands, and in which, after the level display of the signals of all bands and the full band has once stopped, this level display is automatically restored.
In general, in the case where, in the recording of an audio signal, sounds which are unpleasant to the ear, such as a disturbing sound of low, constant frequency and the sound of the wind, are present, it is desirable in some instances to carry out the sound recording with the levels of the frequency bands in which these sounds exist in lowered state. In the reproducing apparatus, furthermore, in the case where the fidelity of the reproduced audio signal is impaired by the effects of characteristics such as the frequency characteristics possessed by the speakers, pickup cartridge, and other acoustical devices themselves and the transmission characteristic of the listening room, it is desirable in some instances to correct the levels of signals of certain frequency bands. In addition, there are instances wherein, for both recording and reproducing, the frequency characteristics are not made flat but are transformed into desired characteristics. In such cases, a graphic equalizer capable of variably adjusting signal level is used for each of the divided frequency bands.
In some graphic equalizers, a calibration scale for indicating the adjustment level is provided interrelatedly with the control knob for level adjustment of each band. With this arrangement, however, while the amount of level adjustment with respect to the input signal can be determined, the level of the signal after it has been level adjusted cannot be accurately determined.
Accordingly, a spectrum display apparatus for level display of each of the divided bands of the signal so as to make possible level adjustment as the spectrum of the signal after it has passed through the graphic equalizer is observed by means of a spectrum analyzer has been proposed. By the use of this apparatus, level adjustment can be accomplished quickly and accurately since it can be carried out while the actual level of the signal being level adjusted is observed.
However, since the level of the input signal varies from time to time, moment by moment, it is considerably difficult to accurately preceive the state of the level at a certain instant of time. Accordingly, in order to perceive the state of the level at any one instant of time, it is desirable that the display of the state of the level at that instant be stopped.
In a known spectrum display apparatus having a spectrum analyzer incorporated therein, the input signal is shifted by means of a shift register of 100 bits, for example, and this is digitally held and supplied to a display drive circuit thereby to carry out level displaying for each of the divided bands.
In this known apparatus, the stopping of the level display is accomplished by holding the shift register. For this reason, after the level display has been once stopped, this state of display is preserved. As a consequence, when normal displaying in accordance with the level variations occuring from time to time, moment by moment is resumed, it has been necessary to terminate the stopped state of the display by operating a switch each time. For this reason, the operation of the apparatus has been very troublesome. Furthermore, since a shift register is used in this known apparatus, in the case where the number of the display elements is increased in order to display the level state in an even finer manner, the number of bits of the shift register must be increased, and problems such as higher cost of production arise.